One of the fastest growing technologies over the last few years has been WLAN devices based on the Institute of Electrical and Electronic Engineers (IEEE) 802.11b standard, commonly known as “Wi-Fi.” The 802.11b standard uses frequencies between 2.4 GHz and 2.5 GHz of the electromagnetic spectrum (the “2 GHz band”) and allows users to transfer data at speeds up to 11 Mbit/sec.
However, a complementary WLAN standard is now coming into vogue. The IEEE 802.11a standard extends the 802.11b standard to frequencies between 5.2 GHz and 5.8 GHz (the “5 GHz band”) and allows data to be exchanged at even faster rates (up to 54 Mbit/sec), but at a shorter operating range than does 802.11b.
IEEE 802.11g, which is on the horizon, is an extension to 802.11b. 802.11g still uses the 2 GHz band, but broadens 802.11b's data rates to 54 Mbps by using OFDM (orthogonal frequency division multiplexing) technology.
Given that the two popular WLAN standards involve two separate frequency bands, the 2 GHz band and the 5 GHz band, it stands to reason that WLAN devices capable of operating in both frequency bands should have more commercial appeal. In fact, it is a general proposition that WLAN devices should be as flexible as possible regarding the communications standards and frequency bands in which they can operate.
Dual-band transceivers and antennas lend WLAN devices the desired frequency band agility. Much attention has been paid to dual-band transceivers; however, dual-band transceivers are not the topic of the present discussion. Developing a suitable dual-band antenna has often attracted less attention. A dual-band antenna suitable for WLAN devices should surmount four significant design challenges.
First, dual-band antennas should be compact. While WLANs are appropriate for many applications, portable stations, such as laptop and notebook computers, personal digital assistants (PDAs) and WLAN-enabled cellphones, can best take advantage of the flexibility of wireless communication. Such stations are, however, size and weight sensitive. Second, dual-band antennas should be capable of bearing the bandwidth that its corresponding 802.11 standard requires. Third, dual-band antennas should attain its desired range as efficiently as possible. As previously described, WLAN devices are most often portable, meaning that they are often battery powered. Conserving battery power is a pervasive goal of portable devices. Finally, dual-band antennas should attain the first three design challenges as inexpensively as possible.
Accordingly, what is needed in the art is a dual-mode antenna that meets the challenges set forth above. More specifically, what is needed in the art is a dual-mode antenna suitable for IEEE 802.11a and 802.11b WLAN devices.